Given a integer String and a integer k, if the length of that string is grater than k, divide it into groups of 3, and then check again if the sum of each groups has length less than k, keep doing this until the length of that String is less than or equal to k.
For Example, String s = "1111122222", k=3; lenth of s =10, which is greater than k
divide the string into 1+1+1, 1+1+2, 2+2+2, 2 = 3, 4, 6, 2 = new String,
new String = 3462, length of new String is 4;
Divide new string into 3+4+6 , 2 = 13, 2 = 132 = new String
since length(132) <= 3 return 132